Principal aim of the present work was a contribution to the development of lead free alloys that may replace high-lead containing solders in electronic applications. Extensive literature search, approximation of melting temperatures, extrapolation of known binary phase diagrams and thermodynamic calculations lead to a selection of more than 50 Al-, Ag-, Mg-, Sn-, Zn- and Bi-based alloys that are potentially applicable as solder material due to their melting range. The predicted melting ranges were veryfied by DSC measurements. 33 alloys were tested with respect to deformation behavior by compression tests. 10 alloys on the basis of zinc or bismuth that showed a sufficient ductility were extruded to thin solder wire. The wetting properties of the remaining alloys were characterised by wetting tests on different substrate materials. Oxidation prevented the wetting of the Zn-based alloys, while the Bi-based alloys showed sufficient wetting. Solder joints of different Bi-alloys were exposed to thermal fatigue load and examined in the ultrasonic microscope for fatigue cracks. The eutectic alloy Bi97,4-Ag2,6 could be identified as potential lead free solder alloy. By increasing the Ag-content up to 12 wt.% and alloying small quantities of further elements the properties were optimized according to the complex requirements for solder alloys in electronic applications. Beside the technological contribution to the development of lead free alloys as alternative to lead-rich solders, in this work also a scientific contribution was attempted in two different areas: first in wires of Zn93-Al6-Ga1 a retarded embrittlement was observed. Investigations by scanning electron microscopy and photoelectron spectroscopy showed changes in the morphology and a strong enrichment of gallium in the fracture surface. Thermodynamic calculations showed that at high temperatures the solubility of the alloy for gallium is high. After extruding the wire at high temperatures the following cooling decreases the solubility and leads to a supersaturation of gallium in the Zn-phase. The supersaturation is then reduced by diffusion of gallium atoms into the grain boundary. The gallium weakens the binding forces in the grain boundary and leads to the embrittlement of the alloy. The kinetics of this mechanism was described quantitatively assuming a simplified geometry. The calculated time frame of the reduction of supersaturation agrees with the observed embrittlement. Furthermore, interesting observations were made in the Ag-Bi-system. The solidification microstructure of the Bi-Ag alloys shows instabilities that were already observed but not explained in the literature. Binary Bi-Ag alloys with different compositions were solidified in experiments with different cooling rates. The formation of the instabilities was studied in the optical and scanning electron microscopes and the dimensions of the cellular structures were quantified. The mechanism for the formation of the instabilities in Bi-Ag-alloys could be clarified: the retrograde solidus line in this alloy system leads to a supersaturation of the silver phase during solidification. The supersaturation is reduced by local remelting. The addition of ternary alloying elements that suppress the retrograde solidusline prevents the formation of the instabilities. The relation between the instabilities at the interface in the solidification morphology and the retrograde solidusline in this system and also in other alloy systems was pointed out in this work for the first time.